Physics, lasers and my wonderful daughter

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Monthly Archives: June 2012

I am planning on attending Frontiers In Optics this October. Although I am taking some time off from research and teaching to be with daughter, I would like to keep up with current research for when I go back to work in optics. This conference seems like a perfect opportunity to do so.

The conference is not for several more months, but they have already started posting information about speakers and special events online. One of the things I think is great about a big conference like this is that I get a chance to learn about a number of interesting topics that are not related to my own research (as well as many that are).

I was looking through the conference program and saw that there is a special symposium on Understanding the Developing and Aging Visual Systems. My own research is very different and I do not know that much about the eye, but I noticed that there are a couple of talks on infant eyes and vision. Ever since my daughter was born, I have been interested in the physics (and optics) of babies, so I immediately looked up some of the speakers.

Richard Aslin, from the University of Rochester, and Rowan Candy from Indian University both had the word infant in the titles of their talks, so I checked out their research web pages. I found out a lot about infant vision and some really fun links.

A few months ago, I wrote about what I can see in my daughter’s eyes. This Tiny Eyes website helps me to better understand what my daughter is seeing with those beautiful, inquisitive eyes. This site is so much fun – anyone with any interest in babies should go there to play. It let me upload a picture of one of my daughter’s toys (I chose her truncated icosahedron of course) and then showed me what this toy would probably look like to my daughter at different ages and different distances from her eye.

To give you an idea of how her vision develops over time, I looked at images of this toy held two feet away from her eyes, at different ages:

You can see how her vision progresses from seeing just a fuzzy blob when she is first born (upper left) to starting to see details around 8 weeks (upper right) to being able to see the toy more like I see it now that she is 10 months old. My daughter became much more interactive and interested in her toys (and less fussy) around 3 months. Maybe this is because she was starting to really see things? Now she likes to roll (bounce, throw, etc.) the ball back and forth.

The research on infant vision is really amazing. Rowan Candy’s group looks at eye movements and the electrical activity in the brain in infants to study the difference between normal and abnormal eye development. Eye tracking and brain imaging using near infrared light help Richard Aslin’s group learn how infants use visual cues in their learning and development.

For those of you less interested in infants, there are many other talks on the imaging and research into eyes and vision (including a plenary talk by Richard Williams on “Imaging Single Cells in the Living Retina”). I have plenty of eye issues myself, being pretty severely near sighted and having two eyes that do not work together, so I find this area of research really fascinating for personal reasons as well as being amazed at the cool optics involved. Sadly, my daughter will likely inherit my (and her father’s) terrible eyes.

Eyes and vision are certainly not my main area of research, and likely never will be, but my main focus has always been teaching and my students love to hear about how optics is related to the human eye. These types of topics get them really excited and motivate them to want to learn more.

Note to Laser Mom readers: I will be posting about Frontiers in Optics from time to time until the conference in October in lieu of my usual articles. Hopefully you will find these topics as interesting as my usual Physics thoughts and will enjoy learning more about the new and exciting things going on in the world of optics.

We moved to CO a few months ago and when we first moved into our new place, I noticed that our front door, which is south facing, became very hot on sunny days. This was March and so I was worried what it was going to be like in summer. Even in March, I was afraid my daughter was going to hurt her hands is she touched it. Interestingly, now it is June, and it is regularly 90 deg and sunny, but the front door stays cool to the touch. This got me thinking about the sun and seasons…

If you have not taken an Astronomy course, you may not spend a lot of time thinking about the solar system and how the Earth moves in relation to the Sun. You may also not have thought much about what causes summer and winter and why the days are longer in the summer.

This week is the summer solstice for the northern hemisphere. The solstice this year is June 20. So what is the solstice, what does it mean about the Earth and the Sun and why do we have seasons? Why does the Southern Hemisphere have opposite seasons?

A common misconception is that summer occurs when the Earth is closest to the Sun and winter occurs when the Earth is farthest from the Sun. Let’s think about that a little more. I found this chart in Lecture-Tutorials for Introductory Astronomy by Edward Prather et al.:

Month

Earth-Sun Distance

December

147.2 million kilometers

June

152.0 million kilometers

September

150.2 million kilometers

March

149.0 million kilometers

There are a couple of things I can learn from this. First, the Earth is not always the same distance from the Sun. Second: It is June now and we seem to be at our farthest point from the Sun. Wait a second! It’s hot now. It’s summer, right? Shouldn’t we be closest to the Sun?

The Southern Hemisphere has winter in June when the Sun is at its farthest point, but the Northern Hemisphere is enjoying summer in June. If the seasons were caused by our distance from the sun, both hemispheres would have to experience summer (and winter) at the same time. But we have opposite seasons, so the distance from the Sun can not be what causes our changing seasons. Well, then, what does?

We know that the Earth is warmed by radiation from the Sun – sunlight. The Earth is also tilted with respect to the Sun at about 23.5°, so that it looks like this as it orbits:

Sometimes the northern hemisphere is tilted toward the sun and sometimes it is tilted away from the sun. When the north is tilted toward the sun, we get more direct sunlight hitting us. The Sun appears to be higher in the sky in the summer when we are tilted toward the sun. Direct sunlight gives us more heat. Think about going for a walk in the summertime. Does the sun feel hotter in the middle of the day when it is directly above or in the early evening when it is low in the sky? The sun definitely feels most intense to me in the middle of the day. I tend to go on walks with my daughter in the morning and the evening.

This more direct sunlight gives us more heat and causes the change in seasons that we experience.

At the north pole, this tilt is enough that in the summer, there is always sunlight hitting the ground and there is no night at the peak of summer. The farther north you are (or south in the southern hemisphere), the more dramatic the change in light and temperature is. Near the equator, there is always plenty of direct sunlight regardless of the season and so the temperature remains warm year round. However, far from the equator, the amount of sunlight hitting the ground changes dramatically due to the tilt of the Earth and so the temperature also changes quite a bit from season to season.

The summer solstice on June 20 is the time when the tilt of the Earth and the rotation around the Sun causes the northern hemisphere to get the most direct sunlight. The sun is highest in the sky in the north and daylight lasts longer than any other day of the year.

So what does this all have to do with my front door? In the spring and winter, the sun is low in the sky to the south and so my front door gets a lot of direct sunlight. However, now that it is summer, the sun is high in the sky and the eaves on the house block the sun from hitting the door. Here is my silly exaggerated picture of this:

Phew! So I do not have to worry about my daughter burning her hand on the door. Of course, it is hotter outside and the sunlight is generally more intense, so I have to worry about other things like sun hats, sunscreen, sun shades on the car, etc. She is very fair of skin (like her mother) and will likely burn easily with the intense summer sun.

We had some visitors come and stay with us last weekend. My daughter is really wary around strangers, so I was very happy that she handled the visitors so well. She relaxed enough to stop giving them the evil eye and went on to smile and play with them some. At one point, one of our visitors mentioned what a nice set of alphabet blocks she had and I was so confused. My daughter doesn’t have any blocks.

I looked up and responded, “Oh, you mean the jingle cubes.”

My husband and I discussed at one point that normal parents probably don’t refer to their child’s toys by the proper geometrical shapes. But these are clearly cubes:

And these very beautiful jingle cubes (they each have a bell inside them so they jingle when my daughter shakes them) were made for us by a mathematician, so I think we should call them cubes.

Of course, geometry has never been my strong point, so I may have to do some research if I want to continue this trend of calling her toys by their right names.

We definitely have spheres (left below), cubes (above), and cylinders (right below) of many different types. Here are a couple:

And of course, it will be important for my daughter to know that this is a ‘truncated icosahedron’: (Mathematica Website)

It has 32 faces and is apparently also the shape used for soccer balls. So this seems important for her to know, right?

My daughter does not have a set of blocks yet, but we are hoping to get her a nice set of wooden blocks, maybe for her birthday. I think I may have to just resort to calling them blocks unless some of my mathematician friends can help fill in the empty place in my brain where geometrical shapes should go.

Of course, at some point, I think we should just call a giraffe, a giraffe and not worry about its shape:

For those of you who are physicists out there, you know that geometrical shapes are not really important since we tend to approximate chickens as point particles and cows as spheres. Anything else is too complicated for us. For those of you who are not physicists and wonder why we care about chickens and cows…well, I am not sure I can explain physics humor, but we think it’s funny. Ah, my poor kid is going to be so embarassed by her mom.

The jingle cubes will always be jingle cubes, though. And they have been a favorite of my daughter’s for a long time. First, they were so big, she needed both hands to grab them and they helped her learn hand coordination. Then, she loved to chew on them (like everything else). Then, her hands grew and her coordination improved so that now she holds one in each hand and shakes them and knocks them together to make music. Maybe soon she will start to stack them, and then (in the distant future) use them to spell words. They really are fantastic, multipurpose jingle cubes.

A couple of weeks ago, I wrote about the solar eclipse that was visible in the Western US. Unfortunately, the weather did not cooperate with my eclipse viewing. I think if I had really tried to see it, I would have been able to see something through the clouds, but there was also a tired and fussy baby involved in the equation.

For those of you who also missed it, a few of my friends posted some pictures of the eclipse on Facebook and gave me permission to share them here:

Or if you’d like to see a time lapse of the entire eclipse, here is one of many YouTube videos.

While I missed the eclipse, there is another exciting solar event coming up: the Venus transit. This is very much like the solar eclipse, only this time, Venus will be blocking the sun instead of the moon. Of course, Venus appears much smaller than the moon to us on Earth, so instead of blocking the entire sun, Venus will just appear as a black dot moving across the sun.

Why does Venus appear so much smaller even though it is actually much larger than the moon? The apparent size of objects in the sky depends on the ratio of the object’s size to the object’s distance from us.

For example, the sun and moon appear to be about the same size in the sky from our viewpoint on Earth. This is why we can have a total solar eclipse where the moon completely covers the Earth. Looking on Wikipedia for estimates of sizes and distances, I find that:

This ratio is almost the same using some average, approximate values for distances. This is why the sun and moon appear to be the same size in the sky when we look up.

So how big will Venus be compared to the sun (or moon)? The Earth orbits the sun at a distance of ~150 million km, while Venus orbits at a distance of ~108 million km. So, when Venus is directly between the Earth and Sun (when we see this Venus transit), it must be ~32 million km away. Venus is approximately the same size as the Earth and so

So Venus will appear much smaller than the Sun. These numbers do not give me a good idea of what this will look like, but this picture from the Wikimedia Commons might help:

This is a fairly small dot, but definitely visible and I am excited about the chance to see it!

We have all probably been told from a young age that we should not look directly at the sun, so how are we supposed to view this transit? The sun is so bright it will actually damage our eyes. There are several different types of methods of looking at the Venus transit (or a solar eclipse) safely. A number of online stores sell “eclipse viewing glasses” which are really just filters that block the sun. The standard set of glasses appears to be made of Optical Density 5 filters. This means that the light that passes through the glasses is 105 (or 100,000) times less than the light that enters the glasses. You can still see the sun through the glasses, but it appears 100,000 times dimmer so it will not damage your eyes. Another good method is to use binoculars, or a telescope or other lens to project an image onto a piece of paper other surface. Do not look at the sun through the lens!!! This would certainly cause you harm! But, if you point the binoculars at the sun and put a surface behind the viewing lens, you will see an image of the sun that you can look at.

The Venus transit will be visible over much of the world, including all of the United States. NASA has a map of visibility if you would like to know if you will be able to see it and when. Click on Local Transit times in the bottom right to find out when you can see the transit at your location. We should be able to see it in the late afternoon/evening of June 5. I am hoping the weather cooperates this time so that we can go out and look! I even got some eclipse viewing glasses for the occasion.

This will not happen again in our lifetimes, so you should try to go out and see it. If you live in a part of the world where the transit is not visible, or the weather does not cooperate, NASA is also broadcasting the transit live from Hawaii so you can watch it on your computers at home.

UPDATE after the Venus Transit:

We were much luckier this past week in our solar viewing. The afternoon was partly cloudy again, but the Venus Transit started around 4 PM and lasted through sunset where we live, so there was a much bigger window during which we could try to find a sunny moment.

As mentioned last week, Venus looks much smaller than the Sun as viewed from Earth and so it was difficult to see the Venus transit just using eclipse glasses and our eyes. We may have been able to project an image using binnoculars or our little telescope, but do not have a fancy telescope and as always, have a little girl who had little patience with this watching the sky nonsense. However, we were able to see the Venus transit using our digital camera with the eclipse glasses in front of the lens. Here are some pictures my husband took:

These both show the image of the sun through the glasses, which filters out most of the light. The black dot is Venus moving between the Earth and sun. The image on the left was taken at 5:58 PM and the image on the right was taken at 7:12 PM. You can see on the right that the clouds have come in, partially blocking the light from the sun.

It was exciting to get a chance to see the transit since it won’t happen again until 2117. If my daughter lives for a very long time, she may get to see the next one, but I am certainly going to miss it!